Provide a mechanism for carrying out a lazy propagation of schedparam
updates to the regular kernel, so that userland does not have to
switch to secondary mode for this.

When userland issues sc_cobalt_thread_setschedparam_ex for updating
the scheduling parameters of a Xenomai thread, a request for
propagating this change to the regular kernel is made pending. Such
request will be committed later, either when:

- the thread relaxes if it is running in primary mode when the update
  request is received;

- next time the thread calls back into the Cobalt core as a result of
  receiving a HOME action from a SIGSHADOW notification, which is sent
  if such thread was relaxed at the time of the update request.

As a result, the target thread will have propagated the schedparams
update to the regular kernel as soon as it resumes (relaxed) execution
in user-space.